Directional Derivatives and Tangent Plane

Draw a 3D coordinate system with a reference point. From this point, construct two lines: one line extends to another point in space, creating a slanted direction; the second line goes in a different direction with its endpoint slightly lower than the start, representing the rate of change along that direction. These two lines illustrate the concept of directional derivatives, and together with a surface or plane, they show the tangent plane at the point. The composition should clearly display the direction vectors, tangent directions, and the relationship between the surface and its tangent plane.